An aide, joining her on a trip to South Carolina in 2008, had procured a salad for his boss while hauling their bags through an airport terminal. But once onboard, he delivered the grim news: He had fumbled the plastic eating utensils before reaching the gate, and the crew did not have any forks on such a short flight.

What happened next was typical: Klobuchar berated her aide instantly for the slip-up. What happened after that was not: She pulled a comb from her bag and began eating the salad with it, according to four people familiar with the episode.

Then she handed the comb to her staff member with a directive: Clean it.

The moment — an abridged version of which Klobuchar recounted herself in a speech to fellow Democrats at the time — encapsulates the underside of life on the Minnesota senator’s team, detailed in interviews with more than two dozen former staff members and internal e-mails reviewed by the New York Times. As Klobuchar joins the 2020 presidential race, many of these former aides say she was not just demanding but often dehumanizing — not merely a tough boss in a capital full of them but the steward of a work environment colored by volatility, highhandedness and distrust.

The senator feared sabotage from her own team: In an e-mail, she once raised the prospect of an in-house mole. She and her top confidantes could complicate the future job opportunities of some staff members who sought to leave, former aides said, sometimes speaking to their would-be employers to register her displeasure. And Klobuchar frequently suggested that her aides were preventing her from greater standing in Washington and beyond, former staff members said.

“We are becoming a joke,” she wrote in one e-mail about the contents of her Twitter feed, “and it is making me a joke.”

Questions about Klobuchar’s actions toward subordinates have shadowed the early days of her 2020 presidential campaign, with articles in HuffPost and BuzzFeed News by turns fueling the hard-driving reputation that has followed her for years in Washington and angering supporters who see sexism in the criticism.

Klobuchar, 58, has allowed that she has “high expectations.”

“Am I a tough boss sometimes? Yes,” she said at a recent CNN forum. “Have I pushed people too hard? Yes.”

Presented with a detailed accounting of the Times’ reporting and the staff e-mails written by Klobuchar, a campaign spokeswoman, Carlie Waibel, said: “The senator has repeatedly acknowledged that she can be tough and push people hard. But these anonymous stories — some of which are just plain ridiculous — do not overshadow the countless experiences of people on the senator’s team who she has been so proud to work with.”

Despite employee turnover that perennially ranks near the highest in the Senate, Klobuchar has defenders among her former staff. She noted at the forum that some people had been with her for many years.

Erikka Knuti, a former communications aide to the senator, described her experience as broadly positive and said Klobuchar could be contrite at times, remembering a gesture of regret from the senator once after she snapped at Knuti in an elevator in front of another lawmaker. “That wasn’t O.K.,” she recalled Klobuchar telling her. “It made me feel valued,” Knuti said.

While there was wide consensus in the interviews that women were often held to a different standard as bosses, former aides — female and male — said their concerns about Klobuchar’s behavior should not be dismissed as gender bias. Many of the aides said they had worked for both men and women, for lawmakers both compassionate and unkind, without encountering anyone else like Klobuchar.

The world of congressional staffs is one of long hours and low pay, with much of the work shouldered by twentysomething junior aides who are learning on the job. Some members of Congress are notorious for round-the-clock phone calls, late-night e-mail and fierce attention to their own press coverage. Klobuchar is among them, but former aides said they were especially troubled by her willingness — in excess of other senators’, they said — to embarrass staff members over minor missteps or with odd requests.

Most of those interviewed for this article — describing memories that span from shortly after her election in 2006 to the much more recent past — discussed their time with Klobuchar on the condition of anonymity for fear of reprisal from the senator. These concerns were not idle, they said. Saving potentially damaging e-mails from Klobuchar became something of a last-day ritual, the aides said, in case they ever needed evidence of her conduct for their own reputational protection.

She was known to throw office objects in frustration, including binders and phones, in the direction of aides, they said. Low-level employees were asked to perform duties they described as demeaning, like washing her dishes or other cleaning — a possible violation of Senate ethics rules, according to veterans of the chamber.

Appraisals of perceived staff incompetence were delivered at all hours of the day and night:

“In 20 years in politics I have never seen worse prep,” Klobuchar said in one e-mail, displeased at how a political event had been handled.

“This is the hands down worse thing you have ever given me,” she wrote in another, questioning her team’s grasp of policy as she rejected its “slop.”

“This is the worst press staff I ever had,” she announced once to employees, according to an aide present. This was effectively a rite of passage, the aide said: The senator had plainly said the same about both predecessors and successors in the office.

Still, while few contest that serving Klobuchar could be a challenge, other current and former aides spoke fondly of the experience, expressing pride over the national platform she has earned. The senator’s defenders say her conduct must be viewed in the larger context of women in Washington, where male leaders with legendary tempers and famously exacting standards, like former President Bill Clinton, have long subsisted atop the political food chain.

For Klobuchar, there is the added complication of tending to a campaign image premised on affable Midwestern common sense.

“The ‘Minnesota nice’ thing is also kind of a double-edged sword,” Knuti said. “In the Midwest you have to be outwardly nice and congenial. But these are tough people. Male senators yell quite a bit. But if a woman yells at you, it’s like, ‘I got yelled at by my mom.’ ”

This much is not in dispute: For years, Klobuchar has had among the highest rates of staff turnover in the Senate, according to a review of congressional offices from the website LegiStorm. Over much of her Senate career, no one outpaced Klobuchar on this score; in 2017, two freshman senators, John Kennedy of Louisiana and Chris Van Hollen of Maryland, surpassed her.

The churn has produced a bit of a vicious circle. Democrats in Washington say she has struggled to recruit and retain top talent. Some operatives say they have shied away from her 2020 campaign, mindful of Klobuchar’s reputation.

Among other concerns, her office’s paid parental leave policy has been described as unusual on Capitol Hill. Two people familiar with the policy said that those who took paid leave were effectively required, once they returned, to remain with the office for three times as many weeks as they had been gone. The policy, outlined in an employee handbook, called for those who left anyway to pay back money earned during the weeks they were on leave.

After receiving questions about the policy from the Times, Klobuchar’s office said it would be revised. “We offer 12 weeks of paid maternity and paternity leave for our staff and have one of the strongest paid leave policies in the Senate,” said a spokeswoman, Elana Ross. “We’ve never made staff pay back any of their leave and will be changing that language in the handbook.” She declined to provide a copy of the current policy as written.

Klobuchar’s supporters say the office environment has never adversely affected her work, cheering her status as a bipartisan pragmatist with a solidly Democratic record and political instincts more moderate than many of her 2020 peers’. They cite her status as a legislative advocate for major national causes like lower prescription drug prices and more local issues like swimming pool safety after a tragic accident in Minnesota.

The senator can also be charming, funny and warm, they say — a fixture at staff weddings and birthday parties. Jonathan Becker, her former chief of staff, said that while Klobuchar could be tough, the intensity was “exhilarating, too,” compelling aides to raise their performance.

“Isn’t that what the American people want in a president?” he said. “They’re not looking for mashed potatoes.”

Others said that Klobuchar often squandered time and mental energy on trivial matters, obsessing over perceived snubs in news media clickbait about who was up or down in Washington and repeatedly suggesting that an inferior staff was standing in her way.

“Senator Leahy, I’m sure he doesn’t put up with this,” she once said of her colleague, Patrick Leahy of Vermont, the longest-serving active senator, according to a person present.

Some former aides who were frequent targets of her ire acknowledged that the senator often had a point, praising her intelligence and political antenna. She has been re-elected in two landslides, including a 24-point victory last year in a state President Trump lost narrowly.

But her blistering feedback to staff was often substantially out of proportion to the offense, these former aides said. Word choice or grammatical issues could make Klobuchar especially furious, not only in prepared text but also in office meetings or common speech. Words like “straight-shooting” and “absolutely” were known to invite her scorn. She urged staff members never to say that another senator “led” something and asked them to call her a “co-sponsor” of legislation instead of a supporter, suggesting that the latter sounded weak.

Klobuchar’s exasperation often appeared connected to two factors: an abiding fear of being embarrassed in front of colleagues or in the press and the conviction that she works harder than her staff.

In one message, in which she said she had not been prepared properly for an event, Klobuchar reminded her team of the hours she kept.

“Please don’t claim lack of time,” she wrote, asking what else might explain their failure. “I flew in at one in the morning. I don’t have that luxury to blame lack of time. Unless YOU were up working at one am, and up again five am the next day, please don’t claim lack of time. That was when I was up.”

In private, she could deliver slashing remarks without particular provocation. Parched one day in the Capitol, she turned to a member of her team and said, “I would trade three of you for a bottle of water,” according to a person who witnessed it.

Former aides said Klobuchar frequently told them they were damaging her political career. On one occasion, a former aide recalled, Klobuchar accused her of “ruining my marriage,” too. (The aide said she interpreted the comment to mean that Klobuchar, in her telling, was forced to work overtime, away from family, to overcome the aide’s failings.)

Many staff members did warmly recall the misery-loves-company camaraderie that built among aggrieved aides. But the core truth of life with Klobuchar was never going to change, they said: She thought she was demanding their best and getting far less. And she was never going to apologize for pointing that out.

“I need to do some serious soul searching about our office,” she said in one e-mail, lamenting the team’s work product. “How can you treat me like this time and time again?”